Patterns of plant species diversity during succession under different disturbance regimes

Summary I suggest that between-community variations in diversity patterns during succession in plant communities are due to the effects of selection on life history strategies under different disturbance regimes. Natural disturbances to plant communities are simultaneously a source of mortality for some individuals and a source of establishment sites for others. The plant community consists of a mosaic of disturbance patches (gaps) of different environmental conditions. The composition of the mosaic is described by the size-frequency distribution of the gaps and is dependent on the rates and scales of disturbance. The life-history strategies of plant species dependent on some form of disturbance for establishment of propagules should reflect this size-frequency distribution of disturbance patches. An extension of island biogeographic theory to encompass relative habitat area predicts that a community should be most rich in species adapted to growth and establishment in the spatially most common patch types. Changes in species diversity during succession following large scale disturbance reflect the prevalent life history patterns under historically common disturbance regimes. Communities in which the greatest patch area is in large-scale clearings (e.g. following fire) are most diverse in species establishing seedlings in xeric, high light conditions. Species diversity decreases during succession. Communities in which such large patches are rare are characterized by a large number of species that reach the canopy through small gaps and realtively few which regenerate in the large clearings. Diversity increases during succession following a large scale disturbance.Evidence from communities characterized by different disturbance regimes is summarized from the literature. This hypothesis provides an evolutionary mechanism with which to examine the changes in plant community structure during succession. Diversity peaks occurring at intermediate levels of disturbance as discussed by Connell and Huston are interpreted in this context.     

Stage of the Estrous Cycle Does Not Influence Myocardial Ischemia–Reperfusion Injury in Rats (Rattus norvegicus)

Even though cardiovascular disease is the leading cause of death for men and women, the vast majority of animal studies use male animals. Because female reproductive hormones have been associated with cardioprotective states, many investigators avoid using female animals because these hormones are cyclical and may introduce experimental variability. In addition, no studies have investigated the specific effects of the estrous cycle on cardiac ischemic injury. This study was conducted to determine whether the estrous cycle stage influences the susceptibility to ischemic injury in rat hearts. Estrous cycle stage was determined by using vaginal smear cytology, after which hearts underwent either in vivo (surgical) or ex vivo (isolated) ischemia–reperfusion injury. For in vivo studies, the left anterior coronary artery was ligated for 25 min of ischemia and subsequently released for 120 min of reperfusion. Infarct sizes were 42% ± 6%; 49% ± 4%; 40% ± 9%; 47% ± 9% of the zone-at-risk for rats in proestrus, estrus, metestrus, and diestrus, respectively. For ex vivo studies, isolated, perfused hearts underwent global ischemia and reperfusion for 25 and 120 min, respectively. Similar to our in vivo studies, the ex vivo rat model showed no significant differences in susceptibility to infarction or extent of cardiac arrhythmia according to estrous stage. To our knowledge, these studies provide the first direct evidence that the stage of estrous cycle does not significantly alter cardiac ischemia–reperfusion injury in rats.Abbreviations: VF, ventricular fibrillation; VT, ventricular tachycardiaCardiovascular disease remains the leading cause of morbidity and mortality throughout the industrialized world, with ischemic heart disease being a major manifestation of cardiovascular disease. Many investigators use animal models to advance our understanding of the etiology and mechanisms involved. Although ischemic heart disease is the leading cause of death for both men and women, the overwhelming majority of studies use male animals. Perhaps the most common reason for this practice is that physiologic fluctuations in female reproductive hormones such as estrogen may be a confounding variable, given the influence of female reproductive hormones on various organ systems.²⁵ Despite the assertion that cyclical variations in female reproductive hormones may confound experimental studies, few data are available that support estrous-cycle–dependent variations in susceptibility to ischemic heart injury.Epidemiologic studies suggest that, compared with men, women have lower cardiac mortality prior to undergoing menopause.⁴⁰ Consistent with human studies, experimental models in several species commonly show that the degree of cardiac injury in young female animals is lower than that in male counterparts.^7,9,21,22,42 Exogenous administration of estrogen has a clear effect in reducing injury,^14,15 but whether endogenous cyclical variations in female reproductive hormones affect cardiac injury is not known.Rats and mice are commonly used species to examine cardiac ischemia–reperfusion injury. Unlike humans, rodents do not undergo menstruation, during which the uterine endometrium sloughs off and is expelled through the vagina, but rather the uterine lining of rodents is reabsorbed during an estrous cycle.²⁴ The rat estrous cycle is typically 4 to 5 d in length and is defined by 4 separate stages: proestrus, estrus, metestrus, and diestrus. Proestrus is characterized by increasing levels of estrogen. At the end of proestrus, ovulation (signaled by luteinizing hormone) occurs and marks the beginning of the estrus cycle. During metestrus and diestrus, the uterine lining regenerates, and the cycle starts again.^24,33 These stages induce changes in the composition of the epithelium of the vagina and the presence of inflammatory cells, which can easily be detected by using vaginal cytology.^18,35We conducted the current study to determine whether estrous cycle stage influences the susceptibility to ischemia–reperfusion injury in the rat heart. Because the stage of the estrous cycle may influence cardiac injury either directly (via a direct effect of circulating hormones), or indirectly (by inducing changes that are intrinsic to the heart), we used both in vivo and ex vivo models of injury.     

Acidic stress promotes a glioma stem cell phenotype

Malignant gliomas are lethal cancers that display cellular hierarchies with cancer stem cells at the apex. Glioma stem cells (GSCs) are not uniformly distributed, but rather located in specialized niches, suggesting that the cancer stem cell phenotype is regulated by the tumor microenvironment. Indeed, recent studies show that hypoxia and its molecular responses regulate cancer stem cell maintenance. We now demonstrate that acidic conditions, independent of restricted oxygen, promote the expression of GSC markers, self-renewal and tumor growth. GSCs exert paracrine effects on tumor growth through elaboration of angiogenic factors, and low pH conditions augment this expression associated with induction of hypoxia inducible factor 2α (HIF2α), a GSC-specific regulator. Induction of HIF2α and other GSC markers by acidic stress can be reverted by elevating pH in vitro, suggesting that raising intratumoral pH may be beneficial for targeting the GSC phenotype. Together, our results suggest that exposure to low pH promotes malignancy through the induction of a cancer stem cell phenotype, and that culturing cancer cells at lower pH reflective of endogenous tumor conditions may better retain the cellular heterogeneity found in tumors.     

Characterization of the mouse liver cell line FL83B

The previously reported mouse liver cell line FL83B has been characterized more completely with respect to its light and electron microscopic appearance, chromosomal composition, and ability to secrete various serum proteins. These cells bear many striking morphological similarities to parenchymal liver cells. Chromosomal analysis showed that the cells were transformed. The ability of these cells to grow in a completely chemically defined medium permitted the unequivocal demonstration of the synthesis of at least 12 mouse serum proteins including albumin and high density lipoprotein.     

HETEROTROPHY OF FOUR MARINE PHYTOPLANKTERS AT LOW SUBSTRATE CONCENTRATIONS1

Three pelagic marine phytoplankters, Coccolithus huxleyi, Skeletonema costatum, and Thalassiosira rotula, and a facultative heterotroph, Cyclotella cryptica, have been exposed to three organic substrates, viz, glucose, acetate, and glutamate, at low concentrations (organic carbon 0.25 mg/liter). Experiments were performed in the dark and light and the net assimilation of substrate was measured by using radiocarbon. The dark uptake of carbon dioxide was also determined, together with photosynthesis at near optimum light intensity. The expected heterotrophy was detected with Cyclotella cryptica. Thalassiosira rotula was found to assimilate glutamate at an appreciable rate. In all cases, however, the short-term uptake of carbon dioxide in the dark was the greatest assimilation rate measured. Values are discussed in relation to their ecological significance and it is concluded that heterotrophic survival of these and probably most other algae in the open ocean would be impossible unless they were in contact with a high concentration of substrate in the form of particulate matter.     

Utilities of gossip across organizational levels

Gossip is a subject that has been studied by researchers from an array of disciplines with various foci and methods. We measured the content of language use by members of a competitive sports team across 18 months, integrating qualitative ethnographic methods with quantitative sampling and analysis. We hypothesized that the use of gossip will vary significantly depending on whether it is used for self-serving or group-serving purposes. Our results support a model of gossip derived from multilevel selection theory that expects gossip to serve group-beneficial rules when rewards are partitioned at the group level on a scale that permits mutual monitoring. We integrate our case study with earlier studies of gossip conducted by anthropologists, psychologists, and management researchers. Kevin M. Kniffin studies cooperation within and among organizations. Kniffin is presently an Honorary Fellow of the University of Wisconsin-Madison’s Department of Anthropology. Kniffin has consulted for a variety of clients, including community-development organizations, labor unions, and credit unions. David Sloan Wilson is an evolutionary biologist interested in a broad range of issues relevant to human behavior. He has authored numerous articles and books, including most recently Darwin’s Cathedral: Evolution, Religion, and the Nature of Society (University of Chicago Press, 2002). Wilson is a professor of biological sciences and anthropology and Director of Evolutionary Studies (EvoS) at SUNY-Binghamton.     

Shyness and boldness in humans and other animals

The shy-bold continuum is a fundamental axis of behavioral variation in humans and at least some other species, but its taxonomic distribution and evolutionary implications are unknown. Models of optimal risk, density- or frequency-dependent selection, and phenotypic plasticity can provide a theoretical framework for understanding shyness and boldness as a product of natural selection. We sketch this framework and review the few empirical studies of shyness and boldness in natural populations. The study of shyness and boldness adds an interesting new dimension to behavioral ecology by focusing on the nature of continuous behavioral variation that exists within the familiar categories of age, sex and size.     

N-(5-chloro-2-(hydroxymethyl)-N-alkyl-arylsulfonamides as gamma-secretase inhibitors

A series of N-alkylbenzenesulfonamides were developed from a high throughput screening hit. Classic and parallel synthesis strategies were employed to produce compounds with good in vitro and in vivo gamma-secretase activity.